ADO.NET DataSet
The DataSet object is central to supporting disconnected, distributed data scenarios with ADO.NET. The DataSet is a memory-resident representation of data that provides a consistent relational programming model regardless of the data source. It can be used with multiple and differing data sources, with XML data, or to manage data local to the application. The DataSet represents a complete set of data, including related tables, constraints, and relationships among the tables. The following illustration shows the DataSet object model.
DataSet object model
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The methods and objects in a DataSet are consistent with those in the relational database model.
The DataSet can also persist and reload its contents as XML, and its schema as XML Schema definition language (XSD) schema. For more information, see Using XML in a DataSet.
The DataTableCollection
An ADO.NET DataSet contains a collection of zero or more tables represented by DataTable objects. The DataTableCollection contains all the DataTable objects in a DataSet.
A DataTable is defined in the System.Data namespace and represents a single table of memory-resident data. It contains a collection of columns represented by a DataColumnCollection, and constraints represented by a ConstraintCollection, which together define the schema of the table. A DataTable also contains a collection of rows represented by the DataRowCollection, which contains the data in the table. Along with its current state, a DataRow retains both its current and original versions to identify changes to the values stored in the row.
The DataRelationCollection
A DataSet contains relationships in its DataRelationCollection object. A relationship, represented by the DataRelation object, associates rows in one DataTable with rows in another DataTable. A relationship is analogous to a join path that might exist between primary and foreign key columns in a relational database. A DataRelation identifies matching columns in two tables of a DataSet.
Relationships enable navigation from one table to another within a DataSet. The essential elements of a DataRelation are the name of the relationship, the name of the tables being related, and the related columns in each table. Relationships can be built with more than one column per table by specifying an array of DataColumn objects as the key columns. When you add a relationship to the DataRelationCollection, you can optionally add a UniqueKeyConstraint and a ForeignKeyConstraint to enforce integrity constraints when changes are made to related column values.
ExtendedProperties
The DataSet, DataTable, and DataColumn all have an ExtendedProperties property. ExtendedProperties is a PropertyCollection where you can place custom information, such as the SELECT statement that was used to generate the result set, or the time when the data was generated. The ExtendedProperties collection is persisted with the schema information for the DataSet.